Existing vehicle wheel steering arrangements include a steering gear, tie rods, control arms, control arm bushings, and wheels. The frictional damping within the steering gear affects both steering feel, which is generally at frequencies less than 2 Hz, and the higher frequency chassis modes, which are typically in the range of 10-15 Hz.
Chassis modes can cause vibration to propagate through the steering gear and result in oscillations of the steering wheel, also referred to as “steering nibble”. Steering nibble is a significant issue for the automotive industry.
Previous steering arrangements relied heavily on frictional damping within the steering gear to attenuate steering nibble energy. This arrangement provides some chassis mode energy dissipation; however, the attenuation may be insufficient because frictional damping becomes less effective at higher frequencies.
Also, the automotive industry trend has been to reduce frictional damping, because decreasing 0-2 Hz damping positively affects customer perceived steering feel. Therefore, any arrangement that relies on increased frictional damping to control 10-15 Hz vibrations will negatively impact steering feel.
Some vehicle steering arrangements have employed a common viscous damper, or dashpot, between the steering gear and tie rod, to add damping to the system to attenuate steering nibble. Viscous devices provide damping across a broad frequency range, even though increased damping is only desired at the steering nibble frequency. Increased damping at low frequencies degrades steering feel, while increased damping at high frequencies transmits more vibration into the passenger compartment. The viscous damper provides this compromised performance as well as a significant cost increase.